In the case of such an electromagnetic valve, the sealing ring serves to minimize unwanted gap leakage flows through the clearance fit between the valve closure member and the valve guide in the direction of the magnet armature chamber and, consequently, of the hydraulic pressure equilibrium of the valve closure member. It is known for electromagnetic valves according to DE 10 2005 049 122 A1 or DE 10 2005 061 509 A1 to be provided with a scaling ring of polytetrafluoroethylene, referred to in short in the following as PTFE, whose contact surface with the valve guide has the surface shape of a spherical segment. As is known, the term spherical segment is to be understood as a geometric body that is produced by removing from a sphere two sphere portions that extend oppositely parallelwise. The intended purpose of this structural design is that the sealing ring, together with the valve guide in the form of a circular truncated cone that is in contact, constitutes a swivel joint in the manner of a spherical joint that affords the valve closure member an angular equalization on the centering valve seat that has as low a resistance as possible, conditional upon component tolerances.
However, practical trials by the applicant have shown that, in the ease of the known designs in respect of the sealing ring to valve guide contact, premature material fatigue of the PTFE sealing ring can occur. The fatigue results in chips on the surface of the material of the sealing ring, which significantly impair its required sealing effect and, consequently, the hydraulic switching function of the electromagnetic valve. The cause of the fatigue is that the actual rotation point of the aforementioned swivel joint is not, as assumed, approximately the central point of the sphere associated with the spherical segment, but is displaced appreciably in the direction of the magnet armature chamber. The result of this is that the valve closure member aligning angularly on the valve seat displaces the sealing ring laterally and presses it, with permanently inadmissibly large forces, against the valve guide.